Focal dystonias are neurological movement disorders characterized by involuntary muscle contractions causing spasms, twisting, repetitive movements, or abnormal postures. Focal dystonias include cervical dystonia, blepharospasm, focal hand dystonia, and spasmodic dysphonia. These disorders can significantly impact quality of life.
Treatment of dystonia has focused on inhibiting the action of alpha motor neurons which cause the muscles to contract in spasm. For example, historically treatment of spasmodic dysphonia has been aimed at paralyzing or weakening one of the vocal folds in order to decrease its ability spasm and interrupt phonation. Dedo first proposed and popularized recurrent laryngeal nerve resection as a treatment for spasmodic dysphonia. This was the first and only surgical procedure which achieved widespread use. Some surgeons did not want to completely transect the RLN, and instead crushed it to weaken or paralyze the vocal folds but keep the nerve intact. Unfortunately, over the long term, the majority of patients who underwent either resection or crush experienced a return of their phonatory spasms. Due to this, both procedures were eventually abandoned.
Botulism toxin (BTX) injection is a common and “gold standard” treatment of dystonia. BTX inhibits neural function, and it is thought that it controls the symptoms of dystonia by preventing the firing of overactive motor neurons.
A few researchers have attempted to use electrical nerve stimulation to treat the symptoms of dystonia. Bidus, et al explored the use of electrical nerve stimulation to treat abductor spasmodic dysphonia by stimulating the motor nerves to the adductor muscle, causing an antagonistic muscle contraction designed to counteract the spasms caused by the disorder.
Tinazzi et al attempted to use low frequency transcutaneous electrical nerve stimulation (TENS) to treat spasms associated with writers' cramp. TENS was delivered to forearm flexor muscles of ten individuals suffering from writers' cramp at a level of stimulation that was below the threshold to cause muscular contractions. The researchers concluded that the TENS treatment may have therapeutic effects on writers' cramp dystonia that lasts for several weeks. The researchers attributed this therapeutic effect to a reshaping of reciprocal excitatory and inhibitory functions between agonist and antagonist muscles, observing that those functions are typically severely impaired in dystonia. Specific muscles were not targeted in this therapy, both because the researchers intended to restore the relationship between agonist and antagonist muscles, which teaches away from the specific targeting of muscles, and because the use of TENS made specific targeting impossible.
Apart from these efforts, the use of electrical nerve stimulation has been primarily used to reanimate paralyzed muscle, not to treat spasmodic disorders such as focal dystonia.